Combining Old School Surveying with New Technology

Wards Island Wastewater Pollution Control Plant (WPCP) is the New York City Department of Environmental Protection’s (DEP) second-largest wastewater treatment plant. It serves over one million people in the western Bronx and Upper East Side of Manhattan. Due to the decommissioning of an existing shared heating plant, the DEP will be constructing a new steam heating system. Heat plays a major role in the wastewater treatment process by stimulating the growth of the anaerobic bacteria that consume organic material in the plant sludge.

The majority of the new steam lines will be installed in a network of existing underground utility tunnels, over one mile long. Normally, plans would be drawn up on paper showing the general path for the new lines to follow. During construction, it would be the contractor’s responsibility to adjust the routing in the tunnel if other pipes or equipment were in the way.

At an old facility like Wards Island, which was constructed over 70 years ago, decades of modifications have resulted in inaccurate and incomplete records of which utility lines exist in the tunnels and where they are located. A contractor would likely encounter many conflicts during construction, thus delaying the schedule and resulting in unforeseen and potentially substantial additional costs.

Innovative Application of New Technology

Erdman Anthony integrated laser scanning technology with traditional surveying to build a three-dimensional (3-D) CADD model of the tunnels and their contents. Through the integration of GPS control, surveying, and laser scanning, Erdman Anthony conquered DEP’s 6,000 linear feet of tunnels with pipes and provided a model that is dimensionally and spatially accurate within a quarter of an inch (1/4"). With the data points generated by 3D laser scanning, Erdman Anthonys experts modeled existing features in the tunnel by fitting geometric shapes. The resulting virtual model was far more detailed than models produced through hand measurementsallowing layout of new pipe routing with no major conflicts.

The 3-D model will allow engineers to lay out the proposed pipes right in the model itself, providing accurate locations and pipe lengths. Essentially, they will "build" the new system in virtual reality.

A State-of-the-Art Process

With traditional methods, a field technician must physically touch the object being measuredoften by crawling under and over pipes with a tape measure. This would have been especially difficult at Wards Island, where over a dozen different pipes, ducts and lines run together in narrow tunnels. Laser scanning eliminates the need for physical contactan obvious safety benefit.

This project included 6000 LF of tunnels, often non-contiguous and running in various orientations. Therefore, separate locations had to be modeled on a common datum in order to maintain the proper spatial relationship to each other. Plus, common scan control points needed to appear in adjacent scans to register them as single data set.

Scanner setups were made every 50 to 60 feet along the tunnels. Each captured at least four scan control points that would be visible in the adjoining scan. Station and offset values for each point were recorded for recovery by the Control Survey Crewoperating at ground level using GPS units to survey control points above the tunnels. GPS was used to tie the horizontal datum to the New York State Plane Coordinate System, Long Island Zone (NAD 83). Elevations were transferred to the control points from site features on the AECOM design plans by digital level, in order to vertically tie the control to Manhattan Vertical Datum.

Points were transferred into tunnels via a plumb bob through surface openings with unobstructed vertical access. A conventional traverse was run through the tunnel to locate the Scan Control Points; when point were registered into one overall data set, they were also translated onto the common project horizontal and vertical datums.

Exceeding Client Expectations

The project is being designed through the New York Power Authority’s (NYPA) Energy Services Programa funding source for projects with energy-saving potential. With the use of survey laser scanning and 3-D modeling, Erdman Anthony has added additional cost-saving potential to this publicly funded project. Time is critical; for every moment between the decommissioning of the existing heating plant and the completion of new construction, a temporary, higher cost system must be operated. Efficient construction will provide greater cost-savings to both NYPA and New York’s residents.

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